The present invention relates to a control system which compensates for temperature changes resulting from sudden changes in the amount of air being supplied to a space.
In typical buildings having variable air volume systems for supplying termperature controlled air to a space, a supply duct is provided for carrying air driven by a fan to the space. A damper is included within the supply duct for controlling the amount of air being supplied to the space and a reheat coil may also be included in the supply duct for reheating the temperature of air being supplied by the supply duct to the space.
The reheat coil may be necessary, for example, in those systems in which a fan system will supply air through a plurality of ducts to a plurality of spaces. The temperature of the air being supplied by the fan system is typically controlled to satisfy the space requiring the most temperature treatment. Thus, the damper to that space may be wide open. The dampers of the other spaces may be at some position in order to control the temperature of the space and the static pressure within the space. A space may have air flow or static pressure requirements which will result in too much cool air (in summer operation, for example) being supplied to the space to meet the temperature requirements of that space. Thus, the flow sensor or static pressure sensor can open up the damper to a sufficient extent to satisfy the air quantity requirements for the space and the reheat coil can be used to elevate the temperature to satisfy the thermostat located within the space.
In such systems, however, conditions can occur which might require sudden changes in the amount of air being supplied to the space. For example, the startup of exhaust hoods, i.e. those which are found in laboratories to exhaust corrosive fumes from the space rather than allowing those fumes to migrate into the space, may require the supply damper to open more to make up for air withdrawn from the space by the exhaust hood. If a simple thermostat is included in the system for controlling the temperature of the space, any temperature change which results from a sudden change in the amount of air being supplied to the space must work its way through the space to the thermostat and then through the thermostat and the control system back to the temperature controlling apparatus before the temperature can be brought back to the desired level. This process can take quite some time. The result is occupant discomfort for the duration of this time. In order to avoid this delay in the temperature control system which is inherent in prior art systems, special provision must be made in order to begin temperature compensation as soon as possible after the sudden change in the amount of air being supplied to the space occurs.